The 2.7 kg/6 lb bike.
The link has much more detail on how they shaved the weight down to this truly unbelievable weight. It is made of unobtainable carbon fiber and every single gram on it is necessary.
I would almost certainly taco this bike in short order because I tend to be pretty hard on my bikes and they either survive or fail. But it is saying something that the state of the art is now able to weigh 6 pounds. That's less than a gallon of milk (which can weigh between 8.5 and 8.8 pounds depending on fat content).
Now if they could build a mountain bike at sub-10 pounds that could be bashed off rocks, roots and trees!